Download CPU Z http://www.cpuid.com/cpuz.php
After you download and install it. Open it you will see a bunch of info about your processor Look at he Instructions line it should say EM64T if your processor is capable of running 64bit.
But just about any processor newer then a P4 600 series will have 64bit. Also if you click on my CPU validator below this message you can see what the program will look like.